Crystal Filter Design

Design

• Butterworth, Chebyshev filters
• Narrow bandwidth bandpass filters for CW or SSB
• 9 MHz nominal frequency
• Several crystal filer designs
• Bin crystals using Colpitts Crystal Oscillator
  • Hand select close values from a pile of crystals
  • Can get much closer than 10% of bandwidth with 50 crystals

W7ZOI Filters

• 9 MHz Filters With Inexpensive Crystals - W7ZOI paper

CW3 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997836
  • 8.997836
  • 8.997838

• 330 Hz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• Modified K&P schematic

• K&P Board

• NanoVNA Capture / Analysis

• Bandwidth
  • 400 Hz -3dB measured
  • 600 Hz -6dB measured

CW 5 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997782
  • 8.997783
  • 8.997784
  • 8.997784
  • 8.997785
• 500 Hz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• XF2 Modifications

• K&P Board
  • Cut etch from X2 to X3
  • Cut etch from X4 to X6
  • Add wire across C1
  • Add wire across C8

• NanoVNA Capture / Analysis

CW3 VS CW5 Filter Comparison

• 5 KHz span
• 5 Crystal filter is wider in bandpass but has sharper skirts than the 3 crystal filter

SSB 4 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997800
  • 8.997801
  • 8.997802
  • 8.997803
• 2KHz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• XF2 Modifications

• K&P Board
  • Cut etch from X1 to X2
  • Add wire across C1
  • Add wire across C8
  • Add wire across C9
  • Install X1 at X1a position

• NanoVNA Capture / Analysis

SSB 6 Crystal

References

• Crystal ladder filters – Software
• Crystal Ladder Filters for All - ARRL QEX
• DISHAL software by DJ6EV
• A Practical Test Set for Comprehensive Crystal Testing
• Crystal characterization and crystal filter design
• Crystal parameters Written by Hans Summers

Kits and Parts dot Com Crystal Filter Kit

• Kits and Parts dot Com Crystal Filter

Schematic

PCB

Notes

• T1 & T2 are optional matching transformers.
• Typical transformer type will be a BN-43-2402 using 34 gauge magnet wire
• C3a,C4a,C5a,C6a are optional trimmer capacitors for fine tuning the crystal filter
• Typical trimmer caps are GKG50015

Videos

Charlie Morris

• Jan '21 - Simple SSB Rig: Part 3 - Crystal Filter

• Mar '20 - CW Rig. Part 1 - Homebrew CW Crystal Filter

• Aug '18 - Homebrew 80/40m SSB/CW Rig - #4b CW Crystal Filter

• Jan '18